This invention relates to a fault tolerant device for controlling a multiple control-point apparatus, such as a robot arm. More particularly, this invention relates to a fault tolerant control system in which redundant processors are used to replace faulty processors.
A multiple control-point apparatus is a device which completes a task as a result of a plurality of independent operations taking place simulataneously. A good example of a multiple control-point apparatus would be a multi-jointed robot arm. For a robot arm to complete a task, its controller must simultaneously generate separate commands for each of its joints. For example, to complete the task of picking up an object, a robot arm controller might have to simultaneously cause a shoulder-like joint to laterally rotate in the direction of the object, cause an elbow-like joint to extend toward the object, and cause a hand-like joint to grasp the object.
Heretofore, various devices for controlling multiple control-point control systems have been developed. See, for example: ACFAS Robot System, Rubbertuators and Applications for Robots, Technical Guide No. 1, Bridgestone Corporation, 1986; Bagchi, S. and K. Kawamura, A Distributed Object-Oriented Robotic System, presented at the 1992 International Conference on Intelligent Robots and Systems (IROS '92), July 1992; Kara, A., S. Bagchi, S. Chawla, M. Iskarous, and K. Kawamura, Intelligent Control of a Robotic Aid System for the Physically Disabled, Proceedings of the IEEE International Symposium on Intelligent Control, pp. 359-364, Arlington, VA. Aug. 1991; and Craig, J. J., Introduction To Robotics Mechanics and Control, Addison-Wesley Publishing Company, Inc., 2.sup.nd edition, 1986.
A significant problem with many multiple control-point controllers is their susceptibility to faults. If one of the control-point controllers becomes inoperative, such as as a result of an electronic fault or a software bug, the entire apparatus may be rendered useless. With an inaccesible apparatus (such as a robotic apparatus employed on a satellite) or a life-critical apparatus (such as a robot used in the care of the handicapped), the cost of the failure of just one control-point controller can be devastating. The instant invention solves this deficiency by providing a multiple control-point controller that is robust with respect to control-point controller failures.
Throughout this application, various publications are referenced. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which this invention pertains.